The representation of complex sounds was examined by comparing both behavioral and event-related brain p potentials (ERPs) to the change or repetition of fundamental frequency (ƒ 0 ) and harmonicity. In the pitch task, p participants were asked to categorize the incoming stimulus as either low or high, regardless of harmonicity, f and in the harmonicity task, participants indicated whether the stimulus was tuned or mistuned, regardless of p pitch. Over three experiments, participants were faster in responding to pitch than to harmonicity. As a result n of this asymmetry, behavioral and ERP data showed that irrelevant changes in harmonicity had little impact on p performance during the pitch task, whereas harmonicity judgments were impeded by irrelevant changes in ƒ 0 . These data are consistent with both general horse-race accounts of processing and specific accounts of mistuning detection that posit prior ƒ 0 registration. In addition, ERP components N2 and P3 were modulated by both intertrial contingency and task instructions, revealing the further influence of top-down mechanisms on concurg g rent sound segregation.